Chatbot using Machine Learning vs Programming
In my view ML does not work very well for conversational AI systems. It is generally alright for intent recognition, so getting what the user wants if they ask a question ("I want to book a flight?", "What is the weather in London?"), but anything after that quickly becomes difficult to handle, especially multi-step conversations that go beyond simple question/answer pairs.

My suggestion would be to plan possible dialogues out as flow charts (more like trees/graphs, as there can be multiple branches at any point), and then write a program that interprets the graph based on user input and gives appropriate replies. You will also want to have some conversational memory to keep track of any information the user has mentioned. That is also tricky to do in a ML system.

For a very simple framework to start off with, have a look at ELIZA. It's half a century old, but you can still use it as a starting point.

(Disclaimer: I work for a company that makes conversational AI systems)